Process for preparation of a sterile suspension of corticosteroid particles for the administration by inhalation

ABSTRACT

A process for the preparation of aqueous suspensions of sterile micronized drug particles, in particular corticosteroid, to be administered by inhalation, which produces homogenous dispersions of particles characterized by optimal size and size distribution is disclosed. The process is carried out by using a turboemulsifier equipped with a high-power turbine and connected to a loading hopper.

The present invention relates to a process for the preparation ofaqueous suspensions of drug particles, to be administered by inhalation,which produces homogenous dispersions of particles characterised byoptimal size and size distribution.

PRIOR ART

The method of delivering drugs by inhalation has been used for severalyears, and is the mainstay of the treatment of diseases that limit therespiratory flow, such as asthma and chronic bronchitis.

The advantages of inhalation over the systemic route include the factthat the drug is released directly at the site of action, thuspreventing systemic side effects and resulting in a more rapid clinicalresponse and a higher therapeutic index.

Among the various types of drug which are administered by inhalation forthe treatment of the respiratory diseases, corticosteroids, such asbeclomethasone dipropionate (BDP), mometasone furoate, flunisolide,budesonide, fluticasone propionate and others are of great importance.They are generally administered in micronised form in suspension, in anaqueous phase that usually also contains surfactants and/or cosolvents,or in a propellant. The drug is inhaled in aerosol form, ie. in the formof a dispersion of solid particles in a gaseous medium. The efficacy ofthis form of administration depends on the deposit of a sufficientquantity of particles at the site of action.

In order to ensure an effective penetration into the low respiratorytract of the patient, i.e. bronchioli and alveoli, one of the mostimportant parameters is particle size, which must be equal or lower than5-6 μm. This size is quantified by measuring a characteristicsphere-equivalent diameter, known as the median aerodynamic diameter(MAD), which expresses the ability of particles to be transported insuspension in an air flow.

Particles with a larger MAD are ineffective because they are depositedin the oropharyngeal cavity, and are therefore unable to reach theterminal branches of the respiratory tree; they can also give rise tolocal side effects, or may be absorbed through the buccal mucosa andgive rise to systemic side effects.

Another important characteristic to ensure correct administration, andtherefore therapeutic efficacy, is homogenous dispersion of theparticles in suspension, without the formation of aggregates whichprevent correct aerosolisation. The formation of more or less compactaggregates can also give rise to problems of distribution and thereforeof uniformity of dose during the filling of the containers. From thetechnological standpoint it is also very important for the particles tofall within the narrowest and most homogenous possible size distributionrange, and to be as finest as possible compatibly with the upper limit(5-6 μm); this because upon variation of environmental humidityconditions, aqueous phase suspensions may face problems over time interms of constancy of particle distribution due to the total or partialrecrystallisation of the small amount of dissolved solute (Davis S et alInt J Pharm 1, 303-314, 1978; Tiano S et al Pharm Dev Tech 1, 261-268,1996; Taylor K et al Int J Pharm 153, 93-104, 1997). As this parameteris inversely correlated with the MAD of the particles, such an increasecan prejudice the efficacy of nebulisation and therapeutic efficacy, asparticles with an MAD exceeding 5-6 μm are unable to reach thepreferential site of action.

Therefore the finer the particles, the lower the probability that afterpartial recrystallisation they will reach the critical size liable toprejudice the properties of the formulation in terms of technologicaland therapeutic parameters.

Another important requirement that must be met by pharmaceuticalformulations for inhalation is sterility. This requirement is becomingmore and more mandatory as confirmed by the FDA final rule “SterilityRequirement for Aqueous-Based Drug Products for Oral Inhalation”published in the Federal Register of May 26, 2000 (65 FR 34082)governing the quality and safety of pharmaceutical products for a numberof reasons, including the fact that the lungs are a particularlyvulnerable organ of the human body, and many patients who use inhaleddrugs have general health problems.

The current trend is to produce inhalation formulations devoid ofpreservatives and bacteriostatics, as it has been reported in theliterature that some of the substances commonly used for this purposecan induce allergic reactions or give rise to irritation of therespiratory mucosae (Menendez R et al J Allergy Clin Immunol 84,272-274, 1989; Afferty P et al Thorax 43, 446-450, 1988). Variousprocesses can be used to manufacture sterile pharmaceutical formulationsfor inhalation. For example, the active ingredient can be sterilised bydry heating or irradiation, followed by preparation of the formulationunder aseptic conditions, or the formulation can be pre-prepared andsterilised by treatment in an autoclave or by filtration.

Some of the sterilisation methods reported suffer from drawbacks orlimitations. For example, heat treatments are unsuitable in the case ofaqueous suspensions of thermolabile corticosteroids such asbeclomethasone dipropionate (BDP), and sterilising filtration is notfeasible for suspensions.

WO 99/25359 relates to a process for sterilising corticosteroids byheating them at lower temperatures than those reported in somePharmacopoeias (110-130° C. vs 140-180° C.) but does not contain anyteaching as to how to prepare the relevant pharmaceutical formulationsin the form of suspensions.

In the patent application WO 00/25746, the applicant described a processfor the preparation of aqueous suspensions for nebulisation based on amicronised active ingredient sterilised with gamma rays.

Said process basically involves a first stage of preparation of anaqueous solution, which constitutes the vehicle and contains suitableexcipients, in a turboemulsifier, followed by the addition of a sterilemicronised active ingredient which in turn is dispersed at atmosphericpressure in the same turboemulsifier. The dispersion of the activeingredient in the aqueous phase may be subjected to an additionalhigh-pressure homogenising treatment which further reduces the averagesize of the particles in suspension.

In the text an example (Ex. 2) of preparation of a suspensionformulation on a pilot scale (100 litres) starting from micronised BDPsterilised by gamma radiation is reported. In said example, the activeingredient is added to the sterile aqueous base and dispersed, initiallyusing magnetic agitation only, then by using a turbine system for 15-20minutes.

However, when this process has been applied on an industrial scale, ithas been found that long processing times are required for thehomogenisation stage. A mixing time of over two hours is required forpreparations exceeding 1000 litres. Moreover, the obtained dispersionsdo not meet the requirement of homogeneity in a satisfactory way.

It has been observed that these drawbacks are largely attributable tothe technological characteristics of the sterile micronised activeingredient, which disperses more slowly as well as more difficulty inthe aqueous vehicle than the unsterilised compound. In fact, sterilemicronised corticosteroid particles must be stored under vacuum tomaintain their sterility, and consequently tend to pack more stronglythan non-sterile particles of the same active ingredient, asdemonstrated by density measurements. Stronger packing is in turnresponsible for difficulties with dispersion.

SUMMARY OF THE INVENTION

A process for the preparation on an industrial scale of aqueoussuspensions for nebulisation comprising a sterile micronised activeingredient, preferably sterilised by irradiation with gamma rays has nowbeen found, and its the object of this invention. The process accordingto the invention reduces processing times and gives rise to suspensionswith a homogenous, reproducible particle distribution and optimumparticle-size distribution, thus producing compositions with a highlevel of physical stability and therapeutic efficacy. Suspensionsobtained with the process according to the invention are used aspharmaceutical formulations for aerosol inhalation after beingintroduced into suitable containers such as multidose vials fornebulisation, and preferably monodose vials.

In the embodiment of the invention, the process is carried out with theuse of a turboemulsifier fitted with a high-power turbine, and ischaracterised in that the active ingredient in powder form istransferred through the turbine by exploiting the vacuum applied in theturboemulsifier. On the contrary, in the prior art, the activeingredient is added from the top directly into the turboemulsifier.

It has now been found that by operating in accordance with the teachingof this invention, i.e. by loading the sterile active ingredient intothe turboemulsifier through the turbine after applying the vacuum ratherthan loading it from the top at atmospheric pressure, far more efficientdispersal of the active ingredient, and therefore homogenous suspensionswith a distribution reproducible from one batch to another, can beobtained in a much shorter time, on an industrial scale. By operatingunder vacuum it is also possible to prevent foam formation, andtherefore the additional operation to remove it. Moreover, it has beenunexpectedly found that finer particles with a narrower, more homogenousparticle-size distribution range can be obtained by the process of theinvention, with no need for further treatments such as treatment in ahigh-pressure homogeniser as described in WO 00/25746. As alreadymentioned, these properties give rise to significant advantages duringthe step of filling the bulk suspension into suitable containers(multidose or monodose vials) and during storage.

In suspensions obtained with the process according to the invention, theparticles sediment more slowly because of their finer size, inaccordance with Stokes' law, expressed by the formula:

$V = \frac{{d^{2}\left( {\rho - \rho_{0}} \right)}g}{18\mspace{11mu}\eta}$

wherein V is the sedimentation rate, d is the mean diameter of theparticles, η is the viscosity of the medium in poises, ρ is the densityof the particles, ρ₀ is the density of the dispersing medium, and g isthe gravity acceleration.

During the container-filling step, the re-circulation conditions towhich the particles of active ingredient are subjected are sufficient toachieve uniform distribution of the particles in the containers, as theypass through the system of radial nozzles of the turbine, and there isno need to use external elements such as pipes or blades to maintain theparticles in suspension. The use of such elements would make itnecessary to open the apparatus periodically for cleaning operations,thus prejudicing continuity of manufacture under sterile conditions. Inthe process of the invention, the particles not only sediment moreslowly, but also are less liable to form agglomerates, which means thatonce introduced into the vials, the suspensions will be more physicallystable, and the storage period can be increased. The formation ofagglomerates, especially “cakes”, ie. sets of highly compact suspendedparticles, can prejudice the correct dosage of the drug, or at leastmake administration less therapeutically effective, as the dose may betransferred incompletely from the vial to the bulb of the nebuliserapparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows the apparatus of the invention of aturboemulsifier combined with a feed hopper;

FIG. 2 shows the particle distribution frequency according to sizeranges, expressed by the Feret diameter determined microscopically: a)obtained by the process according to the invention; b) obtained by theprocess described in WO 00/25746.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described in detail by reference to FIG. 1,which shows a scheme of a plant that can be used for the processaccording to the invention.

A vacuum turboemulsifier (1), constituted by a steel container (2) andfitted with a high-power turbine, and possibly with an agitation system,can be advantageously used to prepare the suspension. “High-powerturbine” means a turbine with a power of between 15 to 55 Kwatts. Aturboemulsifier, which can agitate the suspension via the system ofradial nozzles of the turbine (3), through which the active ingredientpasses, will preferably be used, fitted with a 30 Kwatt turbine.

The system is also equipped with a hopper (4) fitted inside an isolator(5) and connected to the turbine of the turboemulsifier via a rigid pipeor hose (6) for the purpose of loading the powder. The entry of thepowder into the pipe can be regulated by a butterfly valve to minimisethe quantity of incoming air which can contribute to foam formation.“Isolator” means a transparent container, generally made of plexiglas orpolyvinylchloride (PVC), fitted with one or more entrance doors andhandling gloves for transfer of the powder.

The first stage of the preparation process involves preparing theaqueous solution constituting the vehicle in a suitable tank, preferablymade of stainless steel; the solution, which can be sterilised by heator filtration, may contain suitable additives or excipients, preferablyselected from wetting agents such as polysorbate 20 or sorbitanmonolaurate, isotonic agents such as sodium chloride, and optionallystabilising agents such as disodium edetate and/or buffers. The vehicleis preferably sterilised at 121° C. for 20 minutes. If necessary, thesolution thus obtained is subjected to clarifying filtration andtransferred to a turboemulsifier equipped with a vacuum pump. At thesecond stage, after applying the vacuum in the turboemulsifier, one ormore sterile micronised active ingredients are added to the aqueousmedium by introducing them from the loading hopper through the turbine.

Alternatively, the aqueous solution constituting the vehicle can beprepared and sterilisation performed in a turboemulsifier fitted with ajacket suitable both for steam heating and water cooling.

Advantageously, the active ingredient will be a corticosteroid such asbeclomethasone dipropionate, mometasone furoate, fluticasone propionate,flunisolide, ciclesonide or budesonide, micronised by usual processesand sterilised by radiation or heating. Preferably, the activeingredient will be micronised beclomethasone dipropionate sterilised bytreatment with gamma rays under the conditions reported in WO 00/25746.At the third stage, the active ingredient is homogenised, again undervacuum, using the turbine system and operating at a speed of between 750and 4000 rpm, preferably between 1000 and 3600 rpm, and even morepreferably between 1600 and 3000 rpm, for 5-60 minutes, and preferablyfor 20-40 minutes. In the preferred conditions a turbine systemoperating at 2900 rpm for 30 minutes is used.

The suspension of micronised product obtained at the end of thetreatment is distributed into suitable containers, preferablyconstituted by pre-formed monodose vials for nebulisation, optionallypre-sterilised by beta rays irradiation or made with the “blow, fill andseal” technology.

As a consequence, this invention also relates to pharmaceuticalformulations to be used for nebulisation, preferably in unit dosepreparations containing the aqueous suspensions obtained by the processaccording to the invention.

In said formulations, the Feret diameter of at least 90% of thesuspended particles in the final container will advantageously be lessthan or equal to 8 μm. Preferably, the diameter of at least 50% of theparticles will be less than 3 μm, and that of at least 90% less than 7μm. Even more preferably the diameter of at least 50% of the particleswill be less than 2.5 μm, and that of at least 90% less than 6 μm.“Feret diameter” means the distance between imaginary parallel linestangential to a randomly oriented particle and perpendicular to theocular scale (USP 26, 2003, page 2185).

The dimensional characteristics of the particles were also evaluated byusing a Malvern apparatus. This type of test exploits the diffraction ofa laser beam by the particles to determine the size distribution of theparticles in suspension. The parameter considered is the medianvolumetric diameter in μm of 10%, 50% and 90% of the particles,expressed as d(v,0.1), d(v,0.5) and d(v,0.9) respectively, which isdetermined by assuming that the particles have a geometrical shapeequivalent to a sphere. Advantageously, in the suspension formulation ofthe invention, the d(v,0.9) after sonication is less than 8 μm and thed(v,0.5) is comprised between 2 and 3.5 μm. More preferably the d(v,0.9)is less than 7 μm, the d(v,0.5) is between 2.5 and 3 μm and the particlesize distribution (i.e. the difference between d(v,0.9) and d(v, 0.1)does not span for more than 7 μm, preferably for more than 6 μm.

The concentration of active ingredient in the pharmaceuticalformulations according to the invention is between 0.01 and 0.1% w/v,preferably 0.04% w/v in the case of BDP and 0.025-0.05% in the case ofbudesonide.

A further object of this invention is the use of the pharmaceuticalformulations in unit dose preparations containing the aqueoussuspensions obtained by the process according to the invention to treatlung diseases such as asthma and chronic bronchitis with a single dailyadministration.

As reported in the literature for budesonide (Tunek et al. Drug MetabDispos 1997, 25, 1311-1317), it has been found that stable esters of theactive metabolite of BDP, namely beclomethasone-17-monopropionate(17-BMP), are formed in the microsomes of human lung cells withlong-chain fatty acids such as oleic acid.

These esters are retained in the cells much longer than the parentsteroid and release the unchanged active ingredient in a controlledmanner, so that the period of tissue exposure to the drug is increased.

It has also been observed that due to the formation of the monoester inthe lung cells, the elimination half-life and the mean residence time of17-BMP are longer after the administration of aqueous suspensions of BDPby nebulisation than formulations in suspension administered in the formof pressurised aerosols.

This last finding has been attributed to the particle distributionobtained after (re)suspension of the micronised active ingredient in theaqueous vehicle. As it can be appreciated from Table 2 and FIG. 2 ofExample 3 the particles of the sterile micronised active ingredient ofthe aqueous suspension according to the invention are indeed much finerthan those obtained according to the prior art and have a narrower andmore homogeneous particle size distribution too. Said particles can moreeasily dissolve in the lung fluids and penetrate into the cells in abetter way, enabling the active ingredient, due to the formation of theesters into the cells, to persist at the site of action for a longerperiod, so giving rise to a prolonged activity.

As a consequence of the optimal characteristics in term of particle sizeof the suspension formulations achieved by the process according to theinvention, as well as of the behaviour observed for their activemetabolites, pharmaceutical formulations for nebulisation of BDP andbudesonide useful for treating lung diseases with a single dailyadministration can be obtained.

This constitutes a considerable advantage in terms of compliance bypatients.

The invention is more particularly illustrated in the examples below.

EXAMPLES Example 1 Technological Characteristics of MicronisedBeclomethasone Dipropionate (BDP) Sterilised by Irradiation with GammaRays Compared with the Equivalent Unsterilised Product

Sterile micronised BDP was obtained as described in WO 00/25746.

The apparent volumes and densities were measured according to theEuropean Pharmacopoeia, 4th edition, paragraph 2.9.15.

100 g of the test substance is introduced into a dry 250 ml cylinderwithout compacting it. The unsettled apparent volume (Vo) is read off,then 10, 500 and 1250 taps are performed, and volumes (V₁₀, V₅₀₀ andV₁₂₅₀) are read. If the difference between V₅₀₀ and V₁₂₅₀ is greaterthan 2 ml, 1250 further taps are performed (V₂₅₀₀).

Table 1 shows: i) the apparent density before settling (dv), which isthe ratio between weight (g) and volume before settling (ml); ii) theapparent density after packing (ds), which is the ratio between weight(g) and the volume after compacting (ml); iii) packing capacity (Cs),which is the difference between V₁₀ and V₅₀₀ (ml).

The dimensional characteristics of the particles were evaluated by aMalvern apparatus. The results are set out in Table 1.

TABLE 1 Technological characteristics of micronised BDP before and aftersterilising radiation Non-irradiated BDP Irradiated BDP Technologicalcharacteristics dv (g/ml) 0.21 0.32 ds (g/ml) 0.27 0.42 Cs (ml) 16 12Particle size (μm, Malvern) d (v, 0.1) 0.49 0.48 d (v, 0.5) 1.91 1.81 d(v, 0.9) 5.98 5.73

The results demonstrate that after radiation, although BDP does notundergo any variations in particle size, it is packed to a greaterextent than the non-irradiated product, as indicated by the “packingcapacity” value (Cs).

Example 2 Preparation of a Sterile Suspension of Micronised BDPSterilised with Gamma Rays

Composition:

Total amount Amount per Ingredients of the preparation pharmaceuticalunit Sterile micronised BDP 0.6 kg (0.8 mg) Polysorbate (Tween) 20 1.5kg (2.0 mg) Sorbitan monolaurate 0.3 kg (0.4 mg) Sodium chloride 13.5 kg(18.0 mg) Water for injection q.s. for 1500 l (2.0 ml)

The first stage of preparation of the sterile suspension involvespreparing the aqueous base in a Unimix turboemulsifier fitted with a 30Kwatt turbine.

After loading water for injection at 60-70° C. into the apparatus,sodium chloride and surfactants are added, and the preparation is mixedwith the turbine to obtain a homogenous dispersion of the surfactants.

The preparation is then sterilised in a turboemulsifier fitted with ajacket suitable for both steam heating and water cooling; thesterilisation treatment is conducted at 121° C. for approx. 20 minutes.

After filtering and cooling the preparation to the temperature of 30-35°C., a vacuum is applied in the turboemulsifier and the sterile BDP istransferred to the sterile aqueous vehicle through the turbine using thevacuum applied. The active ingredient is dispersed under vacuum alongthe whole homogenisation stage using the turbine system at 2900 rpm for30 minutes.

The turboemulsifier is subsequently connected via sterile piping to thestorage tank of the container-filling machine and positioned underlaminar-flow hood in a controlled-contamination environment, and thesuspension is distributed in monodose vials to the volume of 2.15 mlusing the “blow, fill and seal” technology.

Example 3 Particle-Size Analysis of Preparations Obtained According toExample 2

The dimensional characteristics of the particles were evaluated by usinga Malvern apparatus and by microscopy.

The Malvern tests were conducted as reported in Example 1. The medianvolumetric diameter of the particles was determined before and aftersonication.

For the purpose of examination under the microscope, a drop ofsuspension was placed on a slide and covered with a slide cover. Thediameter of the particles, expressed as the Feret diameter, was measuredwith the aid of a micrometer.

The results, expressed as d(v,0.1), d(v,0.5) and d(v,0.9), i.e. as thediameter in μm of 10%, 50% and 90% of the particles, are set out inTable 2, for the purpose of comparison with those relating to asuspension obtained as described in WO 00/25746.

The data relating to the relative distribution frequency of the particlediameters, measured microscopically, are shown in FIG. 2, forsuspensions obtained with the process according to the invention (a) andaccording to the process described in WO 00/25746 (b) respectively.

TABLE 2 Particle-size characteristics of two sterile suspensions of BDPprepared according to example 2 (Prep. 1) and according to the processdescribed in WO 00/25746 (Prep. 2) respectively. Prep. 1 Prep. 2Particle-size characteristics (μm) (μm) Feret Diameter (microscopy)d(0.1) 0.35 2.04 d(0.5) 1.82 5.75 d(0.9) 5.18 13.89 Median volumetricdiameter (Malvern) without sonication d(v, 0.1) 0.78 1.32 d(v, 0.5) 2.976.54 d(v, 0.9) 7.88 15.94 Median volumetric diameter (Malvern) aftersonication d(v, 0.1) 0.77 0.96 d(v, 0.5) 2.59 4.51 d(v, 0.9) 6.25 11.54

The results shown in Table 2 and FIG. 2 confirm that the processaccording to the invention produces finer particles with a narrower andmore homogenous particle-size distribution.

1. A process for the preparation on an industrial scale of an aqueoussuspension comprising particles of an active ingredient for use as apharmaceutical formulation for inhalation by nebulization, whichcomprises: in a turboemulsifier apparatus comprised of a circularcontainer having a base with an opening therein which receives a turbinedevice and which contains an aqueous solution, equipped with a vacuumpump, and a loading hopper, which contains a sterile micronized activeingredient, connected to said turbine by a conduit: a) applying a vacuumto the turboemulsifier; b) loading the sterile micronized activeingredient into the aqueous solution to form a dispersion of themicronized active ingredient; and c) stirring and homogenizing themicronized active ingredient in the aqueous suspension by operating theturbine, wherein the micronized active ingredient is loaded in theaqueous solution through the turbine, and whereby the median volumetricdiameter of 90% of the suspended particles of the active ingredient isless than 8 micron and that of at least 50% ranges from 2 to 3.5 micron.2. The process as claimed in claim 1, wherein the homogenized suspensionis distributed into containers.
 3. The process as claimed in claim 1,wherein the aqueous solution contains additives or excipients selectedfrom the group consisting of wetting, stabilizing, isotonic andbuffering agents.
 4. The process as claimed in claim 1, wherein themicronized active ingredient is a corticosteroid.
 5. The process asclaimed in claim 1, wherein the aqueous solution has been sterilized byheat or filtration.
 6. The process as claimed in claim 4, wherein themicronized corticosteroid is sterilized by irradiation or by heat. 7.The process as claimed in claim 4, wherein the micronized corticosteroidis beclomethasone dipropionate which is sterilized by being subjected togamma radiation.
 8. The process as claimed in claim 1, wherein thehomogenization of the suspension is conducted at a turbine speed rangingfrom 750 to 4000 rpm for 5 to 60 minutes.
 9. The process as claimed inclaim 8, wherein the homogenization conditions are a turbine speedranging from 1600 to 3000 rpm for 20 to 40 minutes.
 10. The process asclaimed in claim 9, wherein homogenization is achieved at a turbinespeed of 2900 rpm for 30 minutes.
 11. The process as claimed in claim 1,wherein said containers are monodose vials.
 12. The process as claimedin claim 1, wherein the turbine is provided with a radial nozzle system.13. The process as claimed in claim 3, wherein the isotonic agent issodium chloride.
 14. The process as claimed in claim 3, wherein thewetting agent is selected from the group consisting of polysorbate 20and sorbitan monolaurate.